TCP is one of the core Internet protocols on transport layer (AKA OSI layer 4), providing stateful connections with error checking, guarantees of delivery, order of segments and avoidance of duplicate delivery.
This page hosts a formal specification of TCP (Transmission Control Protocol) segment using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for JavaScript generated by Kaitai Struct depends on the JavaScript runtime library. You have to install it before you can parse data.
The JavaScript runtime library is available at npm:
npm install kaitai-structSee the usage examples in the JavaScript notes.
Parse structure from an ArrayBuffer:
var arrayBuffer = ...;
var data = new TcpSegment(new KaitaiStream(arrayBuffer));
After that, one can get various attributes from the structure by accessing fields or properties like:
data.srcPort // => Source port
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
(function (root, factory) {
if (typeof define === 'function' && define.amd) {
define(['kaitai-struct/KaitaiStream'], factory);
} else if (typeof module === 'object' && module.exports) {
module.exports = factory(require('kaitai-struct/KaitaiStream'));
} else {
root.TcpSegment = factory(root.KaitaiStream);
}
}(typeof self !== 'undefined' ? self : this, function (KaitaiStream) {
/**
* TCP is one of the core Internet protocols on transport layer (AKA
* OSI layer 4), providing stateful connections with error checking,
* guarantees of delivery, order of segments and avoidance of duplicate
* delivery.
*/
var TcpSegment = (function() {
function TcpSegment(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
TcpSegment.prototype._read = function() {
this.srcPort = this._io.readU2be();
this.dstPort = this._io.readU2be();
this.seqNum = this._io.readU4be();
this.ackNum = this._io.readU4be();
this.dataOffset = this._io.readBitsIntBe(4);
this.reserved = this._io.readBitsIntBe(4);
this._io.alignToByte();
this.flags = new Flags(this._io, this, this._root);
this.windowSize = this._io.readU2be();
this.checksum = this._io.readU2be();
this.urgentPointer = this._io.readU2be();
if (((this.dataOffset * 4) - 20) != 0) {
this.options = this._io.readBytes(((this.dataOffset * 4) - 20));
}
this.body = this._io.readBytesFull();
}
/**
* TCP header flags as defined "TCP Header Flags" registry.
*/
var Flags = TcpSegment.Flags = (function() {
function Flags(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
Flags.prototype._read = function() {
this.cwr = this._io.readBitsIntBe(1) != 0;
this.ece = this._io.readBitsIntBe(1) != 0;
this.urg = this._io.readBitsIntBe(1) != 0;
this.ack = this._io.readBitsIntBe(1) != 0;
this.psh = this._io.readBitsIntBe(1) != 0;
this.rst = this._io.readBitsIntBe(1) != 0;
this.syn = this._io.readBitsIntBe(1) != 0;
this.fin = this._io.readBitsIntBe(1) != 0;
}
/**
* Congestion Window Reduced
*/
/**
* ECN-Echo
*/
/**
* Urgent pointer field is significant
*/
/**
* Acknowledgment field is significant
*/
/**
* Push function
*/
/**
* Reset the connection
*/
/**
* Synchronize sequence numbers
*/
/**
* No more data from sender
*/
Flags.prototype.toString = function() {
return (this.cwr ? "|CWR" : "") + (this.ece ? "|ECE" : "") + (this.urg ? "|URG" : "") + (this.ack ? "|ACK" : "") + (this.psh ? "|PSH" : "") + (this.rst ? "|RST" : "") + (this.syn ? "|SYN" : "") + (this.fin ? "|FIN" : "");
}
return Flags;
})();
/**
* Source port
*/
/**
* Destination port
*/
/**
* Sequence number
*/
/**
* Acknowledgment number
*/
/**
* Data offset (in 32-bit words from the beginning of this type, normally 32 or can be extended if there are any TCP options or padding is present)
*/
return TcpSegment;
})();
return TcpSegment;
}));